Buy the quoted order: charges the workspace's card on file for the quote's `dueNowCents`, then registers the domains and creates the mailboxes. They arrive connected (no sign-in, `connectedVia: managed`) and warming unless `warmup.enabled` is false, usually within hours; follow the order on GET /mailbox-orders/{id} or the `mailbox_order.completed` / `mailbox_order.failed` webhooks. Send the `quoteId`; the order fields are optional and, when sent, must be exactly what was quoted (`409`, `code: quote-mismatch`). Buying the same quote again returns the same order with no second charge, and an `Idempotency-Key` replays the first answer to a retry. `402` with `code: no-payment-method` or `payment-failed` when the card cannot be charged; `409` with `code: quote-expired`, `price-changed` or `domain-unavailable` when the quote no longer holds (quote again); `409` with `code: payment-pending` when the charge is still being confirmed (the order appears in GET /mailbox-orders within minutes if it went through, so do not buy again); `403` with `code: not-allowed` unless the key's creator may manage billing (owner or admin of the paying workspace). Quoting needs the same right. For `existing` domains: `409` with `code: mailbox-unavailable`, `domain-full` or `domain-admin-cancelled`, and `404` with `code: domain-not-owned`.